SAE technical paper 2008-01-0083, Apr. 14-17, 2008, describes an arrangement consisting of a transmission (CVT) having a continuously variable ratio connected between the engine and gearbox of a vehicle and configured to drive a flywheel through a gearset. The arrangement can add or subtract power to that supplied by the engine.
US 2008/0105475 discloses an automotive vehicle having a powertrain for the vehicle, a flywheel and a continuously variable transmission (CVT) which interconnects the powertrain and the flywheel. When the vehicle decelerates, energy from the powertrain and its associated transmission is transferred to the flywheel. Conversely, energy stored in the flywheel can be transferred to the powertrain in order to accelerate the vehicle.
A typical CVT, suitable for use in a flywheel hybrid vehicle, incorporates a steel belt variator and has a ratio spread of around six. Operation of the CVT is usually under the control of an electronic unit which opens and closes solenoid valves in order to regulate the flow of pressurized oil to the variator.
In a typical flywheel hybrid vehicle, the flywheel can be connected to and disconnected from the continuously variable transmission by means of a clutch. For example, the clutch can be opened while the vehicle is moving at a constant speed and then closed when decelerating, allowing the flywheel to spin up. In another mode of operation, once the flywheel has been pre-charged with rotational kinetic energy, the clutch can be closed so that the vehicle's wheels are driven by the flywheel through the CVT thereby supplementing engine power.
For a smooth operation of a flywheel hybrid vehicle, particularly when handing over between flywheel drive and engine drive, it is beneficial to know the vehicle's mass. Further, in order for any vehicle control system to be able to calculate the amount of additional motive power required from a spinning flywheel which is necessary to accelerate the vehicle up to a desired speed, the mass of the vehicle has to be known. If the vehicle control system is aware of the vehicle's mass, it is aware of the amount of energy that can be recuperated from the vehicle and stored in the flywheel for use at a later time. Hence, this permits efficient management of the vehicle's motive power and hence fuel economy savings can be made. Furthermore, once the vehicle's mass is known, the control system can improve the smoothness of the vehicle's deceleration while recuperating energy (in the flywheel) and likewise, improve the smoothness of the vehicle's acceleration while releasing energy from the flywheel. These possibilities significantly reduce the mechanical wear of the CVT's variator and lead to savings in maintenance costs.
The unladen vehicle mass is known from manufacturer's data. However a vehicle's mass will fluctuate depending on the load which it is carrying at any given time. This fluctuation can be significant in the case of goods/commercial vehicles. The total mass of a commercial vehicle varies between unladen and fully laden and is sometimes even overladen. This means that the ratio between the total kinetic energy of the vehicle at a given road speed compared with the maximum kinetic energy stored in the flywheel can also vary appreciably. A system that does not measure and adapt its operation to this variation will achieve a below optimum fuel saving potential. Furthermore, the driving smoothness during acceleration and deceleration (refinement) will be less than optimal. Lack of driving refinement increases the mechanical strain and wear and tear, ultimately resulting in higher maintenance costs for the operator.
Hence, it would be advantageous to provide a means for measuring any increase in vehicle mass over the unladen mass.